In the past, by using a control circuit such as a microcontroller, a switching power supply circuit has been digitally controlled. There is an advantage that, by digitally controlling, it is possible to precisely control a timing of switching of a switching element and it is possible to implement various functions with software.
In addition, a multi-phase converter in which power supply circuits are connected in parallel is proposed. By deviating phases of switching between the power supply circuits, it becomes possible for the multi-phase converter to reduce a ripple current and to achieve enlargement of a current and a high efficiency. In the multi-phase converter, in many cases a digital control method is used in order to perform precise timing control.
In a power supply device utilizing the digital control method, a control circuit obtains, based on calculation, a value of an output current flowing through a load and uses the value of an output current for controlling an output voltage value and for avoiding an overcurrent. The output current value may be calculated by using a peak current value of an inductance element connected between an output terminal of a power supply circuit and a switching element.
However, calculation for calculating the output current value by using the peak current value is complex, and there is a problem that a load on the control circuit is increased.
The followings are reference documents.    [Document 1] Japanese Laid-open Patent Publication No. 2012-161146,    [Document 2] Japanese Laid-open Patent Publication No. 2004-282842,    [Document 3] Hassan Pooya Forghani-zadeh, “Current-Sensing Techniques for DC-DC Converters”, The 2002 45th Midwest Symposium on Circuits and Systems, 2002, MWSCAS-2002, and    [Document 4] Raghavan Sampath, “Digital Peak Current Mode Control of Buck Converter Using MC56F8257 DSC”, Freescale Semiconductor Application Note, Document Number: AN4716, Rev.1, 05/2013.